Reviews/Vitamin B12/B vitamins reduce stroke
Homocysteine Cardiovascular · VITB12-CV-03 · v2
Borderline: within 4 points of the Likely/Uncertain boundary, so a re-grade could land either side.
Two large, well-run blinded trials found fewer strokes in people given homocysteine-lowering vitamins: HOPE-2 [2],[7] and the Chinese CSPPT trial [3]. But the picture is inconsistent. A trial in high-risk women [4] found no stroke benefit, and a trial in people who had already had a stroke or mini-stroke [6] did not prevent further strokes. The biggest positive result [3] used only folic acid in a population with low folate and no fortified food supply, which may not carry over to countries that add folate to food. The panel judged the effect real but modest and dependent on who is treated, rather than a general result that applies to everyone.
Two double-blind RCTs report a stroke-specific reduction: HOPE-2 stroke RR/HR 0.75 [2],[7] and CSPPT first stroke HR 0.79 [3], even though the broader cardiovascular composite endpoints were null (HOPE-2 primary RR 0.95 [2]). The benefit is not uniform: WAFACS found no stroke reduction with the full B-vitamin combination (RR 1.14 [4]) and VITATOPS did not prevent recurrent stroke (RR 0.91 [6]). Where benefit appears, it concentrates in defined subgroups — low baseline folate and B12 (HR 0.62 [17]), no antiplatelet use [13], elevated cholesterol [15], and older age [20]. NORVIT found no benefit and a trend toward harm from the combination after myocardial infarction (RR 1.22 [1]). The contested point: The evidence divides on whether the positive stroke results reflect a genuine general effect or a context-bound one. The two supportive trials [2],[7],[3] sit against a null combination trial [4], a null recurrent-stroke trial [6], and the fact that the strongest result [3] used folic acid alone in a folate-deplete, non-fortified population.
All 20 papers behind this claim with their DOIs and what each does to it, the panel’s arbitration, the evidence gap map and the open research questions. Free, and sent to your inbox.
We’ll also send you other claims from Vitamin B12, one at a time, and tell you when a release or a pivotal trial changes a grade. Unsubscribe by replying.
One reviewer's only job is to attack the finding. The challenges below were weighed before the grade was set.
The headline stroke reductions are secondary endpoints of trials whose PRIMARY composite endpoints were non-significant (HOPE-2 primary RR 0.95); isolating the one positive endpoint from a null trial risks multiplicity-driven overinterpretation.
The strongest positive result, CSPPT [3], tested folic acid ALONE added to enalapril in a folate-deplete Chinese hypertensive population without mandatory food fortification — not the 'homocysteine-lowering B vitamins' combination the claim implies, and not generalizable to fortified populations.
Where it remains uncertain. The full B-vitamin combination showed no stroke benefit in WAFACS (RR 1.14 [4]) or recurrent-stroke prevention in VITATOPS (RR 0.91 [6]), and the strongest positive result [3] used folic acid alone in a folate-deplete, unfortified population.
Aleatory
Stroke was a secondary endpoint in HOPE-2 [2],[7] and events were few relative to the composite, so chance variation around the estimate is wide.
Epistemic
The strongest result [3] used folic acid alone, so whether the B6+B12+folate combination drives the stroke effect is not resolved by the corpus.
Inferential
Benefit clusters in defined subgroups — low folate/B12 [17], no antiplatelet [13], high cholesterol [15], older age [20] — so inferring a population-wide effect is a stretch from the data.
The load-bearing papers from a corpus of 20, each classified by what it does to the claim. Every DOI is taken from the corpus the claim was graded on.
Large RCT showing a significant stroke reduction, though the primary CV composite was null.
“Fewer patients assigned to active treatment than to placebo had a stroke (relative risk, 0.75; 95 percent confidence interval, 0.59 to 0.97).”
Panel auditInternal validity: high · scope of inference: Adults 55+ with vascular disease or diabetes; stroke was a secondary outcome, primary composite was null.Key limitations: stroke a secondary (not primary) outcome · primary composite not reduced · multiplicity across secondary endpoints
Largest RCT, primary-prevention first-stroke reduction — but folic acid alone, folate-deplete Chinese population.
“the enalapril-folic acid group had a significant risk reduction in first stroke (2.7% of participants in the enalapril-folic acid group vs 3.4% in the enalapril alone group; hazard ratio [HR], 0.79; 95% CI, 0.68-0.93)”
Panel auditInternal validity: high · scope of inference: Chinese hypertensive adults without prior stroke or MI, in a country without folic acid food fortification and low baseline folate.Key limitations: folic acid only, not full B-vitamin combination · low-folate unfortified population may not generalise · no comparator without enalapril background
Counter-evidence: full B-vitamin combination gave no stroke benefit in high-risk women despite homocysteine lowering.
“stroke (41.9/10,000 person-years vs 36.8/10,000 person-years; RR, 1.14; 95% CI, 0.82-1.57; P = .44)”
Panel auditInternal validity: high · scope of inference: High-risk US women (health professionals) aged 42+ with CVD or multiple risk factors.Key limitations: stroke a secondary outcome · point estimate numerically favours placebo · women-only high-risk cohort
Only the composite primary endpoint is reported (risk ratio 1.08 for folic acid + B12); the abstract gives no stroke-specific effect estimate.
Panel auditInternal validity: high · scope of inference: Secondary prevention in patients within 7 days of acute myocardial infarction.Key limitations: composite endpoint, stroke not isolated · post-MI population only · trend toward harm in triple-therapy arm
4 of 20 papers shown. The full review lists all of them, with the panel’s arbitration →
Claims are graded at each quarterly release, and re-graded between releases only when a pivotal trial lands. Every change is a new version of the claim.
Replicated RCT evidence supports a modest stroke-specific benefit, but null trials, subgroup-confined effects, and the folic-acid-alone confound keep it short of established.
Release 2026-q4 re-graded every claim from its corpus under protocol v0.19. An earlier release's grade is shown for the record; it came from an earlier protocol and is not a movement.
Assumptions that carry weight but are not themselves established.
The panel records the gap that would most move the claim, and the study that would close it.
Combination B vitamins with stroke as primary endpoint. The positive stroke signals are secondary endpoints of trials whose composites were null [2],[4]; no trial in the corpus powers stroke as its primary endpoint for the full combination. The panel rates this the highest-importance open gap for the claim, and names the study design that would close it: A double-blind RCT of folic acid + B6 + B12 with first or recurrent stroke pre-specified as the primary endpoint and adequate event counts.
Open question: Does the full homocysteine-lowering B-vitamin combination reduce stroke when stroke is the pre-specified primary endpoint? Why it is still open: Supportive results [2],[7] are secondary endpoints of null-composite trials, and the combination was null on stroke in WAFACS [4] and VITATOPS [6].
Priors is a sceptical first reader, not peer review, and not medical advice.
Release 2026-q4 · graded 18 Sep 2026 · protocol v0.19